A-LevelBiologyImmunity9700/22 · Feb/Mar 2024 · Q68 Marks

Fig. 6.1 is a simplified diagram representing a section through the human immunodeficiency virus (HIV) particle that causes HIV/AIDS. The diagram shows the virus particle about to attach to the cell surface membrane of a T-helper cell at a receptor protein called CD4. A second protein (coreceptor) called CCR5 is also necessary for the virus particle to enter and then infect the T-helper cell. [Figure 6.1]

(a)Identify structure X in Fig. 6.1.[1]
(b)Explain how the ability of the immune system to resist the damaging effects of a pathogen is affected by destruction of T-helper cells.[3]
(c)Studies have shown that some individuals did not become infected with HIV even though they were repeatedly exposed to the virus. Later discoveries indicated that these individuals had a mutation in the gene for the CCR5 coreceptor protein. Suggest how mutation of the gene for the CCR5 coreceptor protein provided protection against HIV infection.[1]
(d)The use of monoclonal antibodies against the CCR5 coreceptor protein (anti-CCR5) has been shown to be effective in the treatment of HIV infection. Outline how anti-CCR5 monoclonal antibodies can be synthesised in the laboratory using the hybridoma method.[3]

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Mark scheme

Marking points from the official mark scheme (Feb/Mar 2024). The mark or mark type is shown in brackets.

[1] 6(a) capsid; A capsomere or protein coat R protein / glycoprotein / caspid
[3] 6(b) accept accounts based on primary and/or secondary immune response .
fewer cytokines released ;
and any two from:
fewer plasma cells, so fewer antibodies produced ; A B lymphocytes
fewer macrophages stimulated / less production of 'angry' macrophages / AW / less antigen presentation by macrophages ;
fewer T-killer cells stimulated to divide / less T-killer cells / less infected cells killed (by T-killer cells) ;
fewer memory cells (produced by the primary response);
AVP;
[1] 6(c) virus cannot enter the T-helper cell / CCR5 unable to trigger endocytosis of viral particle ;
[3] 6(d) any three from:
1 (named) small mammal, injected / AW, with CCR5 ; A antigen
2 immune response occurs (over several weeks) ; A immune response described
3 plasma cells / B-lymphocytes / B-cells / splenocytes, extracted from spleen ;
4 plasma cells / B-lymphocytes / B-cells, fused with, myeloma / tumour / cancer / AW, cells (to form hybridomas) ;
5 screening / selection / AW, for hybridomas producing desired, (monoclonal) antibodies ;
6 AVP; e.g. hybridoma cells separated (into wells) to produce clones
ref. to large scale production

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